Known runflat devices are generally constituted by a support ring which is mounted with some clearance about a wheel rim inside a tire cover. Said ring, constituted by a flexible material, is in a single piece and because of its width at its base, it exerts a force to flatten the tire on the rim. Occasionally, rigid devices in a plurality of pieces or sectors are fixed one to another.
Japanese patent document JP-A-03 231007 discloses a runflat device for mounting around a wheel rim of the multi-piece type, comprising:                a metal ring divided into a plurality of arcuate sectors connected together in pairs and with an axial section in the shape of an “I”, each vertex of which is designed to support a tire when running flat, and in which the lateral flanges of each base are trapped in a metal anchor element which is also arcuate in shape; and        an annular rubber sole which includes a circumferential recess the lateral flanges of which grip around said anchor element and which is designed to be mounted on the rim against the beads of the tire, to wedge said beads against the flanges of the rim.        
A major disadvantage of that runflat device is that its weight is relatively high, which makes mounted assemblies incorporating it heavier and thus renders vehicles equipped with such assemblies heavier. This overall increase in weight is particularly deleterious as regards the cost of transporting vehicles by air.